1. Field of the Invention
The present invention relates to an apparatus and method for attenuating high energy radiation.
2. Description of the Related Art
At cross border immigration checkpoints, x-ray monitoring systems are sometimes used for conducting security inspection of vehicles, including motorcycles. During the inspection process, drivers and passengers of the vehicles or motorcycles are exposed to the high energy radiation of the x-ray source.
While the high energy radiation emitted by the x-ray source for such x-ray monitoring systems is usually rated safe for humans, psychologically, people are uncomfortable with being x-rayed. Furthermore, for those who commute across borders frequently, their health risks due to high energy irradiation are inevitably increased. Privacy is also an issue as the X-ray images captured would show up naked images of people.
At times, a higher dosage of x-ray is required for monitoring vehicles having bodies with high energy radiation filtering properties, for example, cargo-containing parts of the vehicle. To eliminate the risk of exposing humans to the higher dosage of high energy radiation, some of the x-ray monitoring systems are designed to perform screening without the presence of the drivers/passengers. Drivers/passengers have to exit the vehicle. This is not a good solution as it would cause delays at the checkpoints.
Another solution, PCT publication WO 2009/106815, provides more than one x-ray sources with different energy outputs. High energy scanning from a High energy x-ray source is turned on for scanning a cargo-containing part of the vehicle and Low energy scanning from a Low energy x-ray source is used for scanning that part of vehicle occupied by a human or animal. The x-ray sources are turned on and off appropriately. Alternatively, the human or animal occupied part of the vehicle is not scanned at all. It is appreciated that x-ray sources take time to be energized after they have been switched off. It is questionable whether the x-ray source could energize fast enough to avoid undue delay. Furthermore, it is also appreciated that having more than one x-ray sources is costly.
X-ray monitoring systems are also widely used in the medical field. It has been observed that only selected parts of x-ray images of patients taken using conventional x-ray machines, only selected parts are required for medical diagnosis. The other parts of the images are redundant thus indicating that the patient was subjected to high energy radiation unnecessarily.